Laminar flow air hood apparatus



P 1966 w. .J. WHITFIELD LAMINAR FLOW AIR HOOD APPARATUS 5 Sheets-Sheet 1 Filed Dec. 24, 1963 INVENTOR. Will/ls J. Whitfield 4 "am ey Sept. 20, 1966 w. J. WHITFIELD LAMINAR mow AIR Boon APPARATUS 5 Sheets-Sheet 2 Filed Dec. 24, 1963 INVENTOR. Will/s J. Whitfield x E a n I 0% 7 R x u I 4 V 4 I 3 Q 2 m 1 A A Home) sept' 1966 w. J. WHITFIELD LAMINAR FLOW AIR HOOD APPARATUS 5 Sheets-Sheet 3 Filed Dec. 24, 1963 INVENTOR. Wi/l/s J. Whitfield A from y United States Patent 3,273,323 LAMINAR FLOW AIR HOOD APPARATUS Willis J. Whitfield, Albuquerque, N. Mex., assignor, by

mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Filed Dec. 24, 1963, Ser. No. 333,235 Claims. (Cl. 55-385) The present invention relates generally to vented work stations and more particularly to air hood assemblies contributing advancements or improvements over dust-free devices such as disclosed in applicants copending United States application, Serial No. 194,740, filed May 14, 1962, now Patent Number 3,158,457, issued Nov. 24, 1964.

In Working with toxic, including radioactive, fluids or solids, by themselves or in association with other materials, it is usually preferable to isolate workers from. these toxic substances or agents such as by venting or exhausting the noxious fumes emitting from the latter while simultaneously affording access by the workers arms or other tools to the area containing the toxic agents. Normally this isolating should be accompanied by a high or other degree of cleanliness, as by controlling the quantity of particulate matter in the area or proximity of the toxic agents or other materials for preventing them from being contaminated with airborne contaminants. As pointed out in great detail in applicants above identified copending application, the quantity of airborne particulate matter in an environment where complex mechanisms are being assembled or otherwise worked upon is indeed an area of great concern. Thus, if the substances associated with toxicity must also remain free of contamination from airborne particulate matter, then a somewhat complex problem presents itself because of the health hazards involved.

It has been found that in most instances the apparatus heretofore used to vent noxious fumes from a working area suffered several shortcomings or drawbacks which detracted from their usefulness. For example, most fume hoods or the like are not operable independently of the area in which they are located in that they function as venting systems by drawing air into the interior of the hood from adjacent areas. Normally this air is pulled or aspirated directly into the working volume of the hood through an access opening or, in some instances, may flow through special openings in the body of the hood. However, with either flow the air pulled into the hood interior or working volume is laden with excessive airborne particulate matter from the areas surrounding the hood. While this arrangement appears unsatisfactory it should be kept in mind that the air within the hood bearing the noxious fumes from the contained toxic agents may escape into the surrounding area and be hazardous to the health of the workers if this air is not properly exhausted from the hood. Consequently, the presence of this excessively contaminated air within the working area was heretofore considered an inevitable penalty in view of health requirements.

Thus, an object of the present invention is to provide ingress and egress to a work area which may contain toxic substances while simultaneously maintaining the work area substantially free of airborne particulate matter.

Another object of the present invention is to provide a ventilating system with open access thereinto that is capable of preventing contaminated fluids within the system [from escaping through the access opening.

A further object of the present invention is to utilize in a vented hood assembly a continuously moving mass of clean air having substantially uniform velocity along parallel flow lines throughout substantially an entire working volume.

'ice

A further object of the present invention is to provide improved means for selectively varying the volume of air being exhausted from a ventilating system.

Other and funther objects of the invention will be obvious upon an understanding of the illustrative embodiments about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

Preferred embodiments of the invention have been chosen for purposes of illustration and description. The preferred embodiments illustnated are not intended to be exhaustive nor to limit the invention to the precise forms disclosed. They are chosen and described in order to best explain the principles of the invention and their application in practical use to thereby enable others skilled in the art to best utilize the invention in various embodiments and modifications as are best adapted to the particular use contemplated.

In the accompanying drawings:

FIG. 1 is a perspective view of a preferred form of the present invention;

FIG. 2 is a side elevational view showing in section the general arrangement and details of the air moving system;

FIG. 3 is a sectional front elevational view taken generally along line 33 of FIG. 2;

FIG. 4 is a fragmentary view showing the relationship of an air filter to an interior wall;

FIG. 5 is a fragmentary sectional view showing a modified form of the present invention;

FIG. 6 is a fragmentary sectional View showing another modified form of the present invention; and

FIG. 7 is a fragmentary sectional View showing still another form of the present invention.

Referring to FIGS. 1-4, the present invention comprises a cabinet or housing 10 shown in a generally rectangular configuration and defined by a front Wall 11, side walls 12 and 13, rear wall 14, and upper and lower end walls 15 and 16 respectively. The housing 10 includes therein a working volume or work area 18 disposed intermediate the end walls 15 and 16 and partially encircled by the side walls 12 and 13 and the rear wall 14. In the front wall 11 there may be an opening. 19 in registry with the work area 18 and having vertical and horizontal dimensions substantially similar to those of the work area 18 as will be hereinafter set forth.

The housing 10 may be sub-divided by partition means into several spaces, compartments or chambers including the work area 18. One of these partition means may be generally parallel with and disposed above the lower end wall 16 at a location adjacent the lower end of the opening 19 and extend between the walls 11, 12 and 14 such as to form a platform or floor 21 in the work area 18. Another partition means 22 may be disposed at a location intermediate the floor 21 and the lower end wall 16 and extend between walls 11, 12 and 14. The partition means 22 and the floor 21 may terminate at a location inwardly spaced from wall 13 and below a vertical edge of the opening 19 where they intercept or join an upright partition 24 extending between the front wall 11 and rear wall 14. This partition 24 has an upper end thereof terminating at a location below the upper end wall 15 such as to place the work area 18 in registry with the opposite side of the partition 24 for enabling a mass of air flowing upwardly in the space formed between wall 13 and partition 24 to be directed into the work area 18 as will be described in detail below.

The ceiling of the work area 18 may be defined by an air filter 25 which substantially fills the cross-sectioned space between the walls 11, 12, and 14 and the partition 24. The air filter 25 preferably lies on a horizontal plane essentially parallel with the floor 21 such that both the floor 21 and the air filter are at right angles to the walls 11, 12 and 14 and the partition 24. This arrangement and relationship of the air filter 25 to the floor, walls and partition set forth a desirable [feature in that the air passing through the filter 25 is directed vertically downwardly into the work area 18 as a body or mass of air with each minute portion thereof moving at essentially the same velocity as every other minute portion, along substantially parallel flowlines or, in other words, with laminar air flow characteristics.

'It has been found that such laminar air flow through a working volume is highly desirable because of its isolation properties, i.e., with the body of air moving at essentially uniform velocity along parallel flow lines, turbulence which normally causes random air flow is substantially non-existent. Thus, by utilizing a laminar air flow system, a portion of .a side wall may be removed, such as represented by the opening 19 in wall 11, while maintaining an air flow across the work area without effecting air flow out of the Work area 18 through the opening 19, unless such flow is desired as will be described in greater detail below.

In order to fabricate a laminar air flow system, it has been found that the air inlet into the work area should have a cross-sectional area substantially equal to the crosssectional area of the work area 18. To provide the desired cross section at the air inlet, which is normally occupied by the air filter 25, the air filter 25 may be so constructed that its effective or air filtering section 27 is centrally oriented in a supporting framework 28. The framework 28 surrounding the air filtering section 27 may then be isolated from the referred to cross sections by placing a lining or upright walls 30, 31 and 32 about the work area 18 at locations closely adjacent side wall 12, rear wall 14 .and partition 24 respectively. These upright walls -32 may be of any suitable material with smooth surfaces, such as, for example, stainless steel and the like, and be so oriented that their interior surfaces are essentially flush with the inner surface of the framework 28, thus providing the work area with a cross-sectional area essentially equal to the effective area of the air filter. It may be desirable to place a seal 34 of foam rubber or the like between the uppermost ends of the walls 30-32 and the air filter framework 28 so as to prevent undesirable air flow into the work area 18, mg, dirty air bypassing the filter 25 and air currents tending to create turbulence (FIG. 4).

'It may be preferable to use highly efficient fine or sub micron filters capable of cleaning the air passing therethrough until there are less than 1000 particles of dust or other contaminants greater than about 0.32 of a micron in diameter per cubic foot of space in the work area 18 (a micron equals approximately one forty-millionth of an inch). One such filter found satisfactory is the commercially available Absolute filter manufactured by Cambridge Filter Corporation of Syracuse, New York. The Absolute filter is capable of filtering out of a passing air stream 99.97 percent of all particulate matter above about 0.32 micron in diameter. Of course, other sub-micron air filters may be used if desired, but the feature of passing ultra-clean air from an Absolute filter or the like into a work area is highly advantageous and should be retained if maximum benefits are to be derived from filtering the air prior to its entering a work area.

With the air filter 25 in place, which may be by any suitable arrangement, e.g., supporting it by or fastening it to the walls 11, 12 and 14 and partition 24, suspending it from the top end wall '15, or the like, a plenum chamber 33 is formed intermediate the filter 25, end wall 15, walls 11, 13 and 14, and the partition 24. This plenum chamber 33 is arranged to received air from an air moving assembly and convert the dynamic flow to a relatively static flow at a pressure greater than ambient pressure as will be described below.

As the laminar flow of ultra clean air traverses the vertical length of the work area 18 it picks-up airborne particulate matter and noxious fumes given oil? by substances within the work area 18. Thus, in order to exhaust this captured airborne particulate matter and noxious fumes without causing them to fiow out theopening '19 into areas adjacent the ventilating assembly, the floor 21 may be provided with a sufficient number of passageways or apertures thereth-rough to receive the downwardly flowing air. For example, the floor 21 may comprise a metal grating 35 of the necessary thickness or strength for supporting objects or substances within the clean work area 18. Also, if working upon relatively small articles or mechanisms it may be desirable to place a perforated metal plate 36 over the grating 35 to provide an adequate supporting base for these articles or mechanisms. It has been found that openings or perforations through the metal plate 36 comprising about thirty percent of the plate area facilitate reception of the downwardly moving air flow under most conditions. The grating 35 and the metal plate 36 comprising the floor 21 may be releasably supported or carried by the walls and partition in any desired manner, e.g., a metal fiange arrangement as indicated at 37.

After the contaminated .air passes through the floor as indicated by the arrows in FIGS. 2 and 3, it is receive-d in the chamber or compartment 38 defined by the partitions 22, 24, walls 11, 12 and 14, and the floor 21. From this compartment 38 the contamianted air and other products may be discharged to a suitable external location.

As described above, the work area 18 is completely enclosed on three sides with ingress and egress of the area being provided through the opening 19 in the front wall 11. The size of this opening may be readily varied to any desired size by a vertically displaceable door or panel 40 which may preferably be in the form of a transparent window of glass or the like so as to permit visual access to the entire work area 18. This panel 40 may be mounted in a suitable frame 41 of metal or the like and be counter-balanced by well known techniques (not shown) to facilitate the opening and closing of the panel. It may also be desirable to place a suitable seal (not shown) between the outer surface of the wall 11 and the inner surface of the panel 40 .at a location adjacent the air filter so as to prevent escape of noxious gases or other products or the aspiration of contaminants.

In order to provide the flow of the ultra-clean air through the work area and the subsequent expelling of the contaminated air from the ventilating system, a pair of blowers 43 and 44 may be used with blower 43 supplying air to the system while blower 44 exhausts air from the system. These blowers 43 and 44 may be located adjacent one another in a compartment 45 provided between partition 22 and the lower end wall and may be mounted in operable positions by any suitable means such as by the motor mountings shown in FIGS. 2 and 3. Air for the supply blower 43 may enter the compartment 45 through an opening 47 in the front wall 11 or at any other suitable place. The opening 47 may contain a rough air filter 48 or, in other words, an air filter of lesser efficiency than the super interception or sub-micron air filter 25. The air filter 48 may be held in any suitable manner such as by a removable grill-like cover 49 (FIG. 1) and be of any suitable commercially available type capable of preventing the passage of about to percent of all particles between about 10 to 20 microns in size. Thus, the primary function of the air filter 48 is not to thoroughly cleanse the air, but to catch large airborne particulate matter and thereby prevent such particulate matter from clogging the sub-micron air filter 25 which would necessitate frequent changes of this more expensive air filter.

The supply blower 43 pulls air through the air filter 48, into the air moving portion, e.g., a centrifugal .fan or the like, and thence via an air conveying duct or conduit 50 into the plenum chamber 33. This air being discha ged by the blower 43 has a dynamic pressure due to its initial velocity, but as the air enters the plenum chamber its movement is substantially slowed such as to form a relatively static body of air under a pressure of say, about one-half inch water in the plenum chamber.

With a quantity of air under static pressure in the plenum chamber 33 and with the air filter 25 providing resistance to air flow, a pressure drop of the air flowing through the air filter 25 is effected to assure that the volume and velocity of air passing through the filter are substantially equal throughout all portions thereof. This flow pattern of the air through the air filter is primarily responsible for initiating the laminar flow, but it is generally up to the walls or lining to maintain the laminar flow characteristics. A unique feature afforded by this essentially turbulent-free laminar air flow arrangement is that the air makes only a single pass through the work area 18. Consequentially, the particles or fumes captured by the downwardly flowing air are directly carried from the work area 18 rather than having these contaminants flowing in random directions throughout the work area 18 such as would normally be the case if sufficient eddies were preesnt. Also, if laminar flow conditions are initially present, obstructions created by the various materials and workers arms or tools will not seriously affect the clean 'liness of the work area 18 or disrupt the laminar flow.

Another feature in the unique positioning of the air filter 25 with respect to the work area is the large area of the filter 25 exposed to the work area through which a tremendous quantity of air may be passed while maintaining acceptable levels of air velocities in the work area as will be described in detail below.

The air upon vertically traversing the work area may be drawn through the openings in the floor 21 and into the compartment 38 by the exhaust blower 44. This blower 44 may comprise an air moving portion with its inlet air duct 51 in registry with the compartment 38 and its outlet air duct 52 extending to a location external of the cabinet where the duct 52 may be coupled to a suitable air cleaning and discharging system (not shown). By utilizing the exhaust blower 44 in registry with the compartment 38 it is assured that the contaminated air and other products picked up by the air stream are drawn into the compartment 38 and subsequently disposed of rather than having these contaminants pass from the work area 18 through the opening 19. Also, the suction effect provided by the exhaust blower 44 aids in maintaining laminar flow conditions within the work area 18 since obstructions due to air pockets or the like are minimized.

It may be desirable to provide the exhaust blower 44 with a variable capaicty feature such as by placing a manually or automatically operated damper 54 in the air duct 52. With the blower 44 discharging air at preselected rates the air flowing through the work area may be placed in a balanced flow condition, air inflow condition, or an air outflow condition. In a balanced fiow condition the damper 54 is adjusted so that the blower 44 is drawing air from the work area at essentially the same rate as the air is being supplied to work area by the supply blower 43. During this flow condition the ultra-clean air emerging from the filter 25 passes by the opening v19 and into the floor 21 without mixing or mixing very slightly with the air outside the work area. The air inflow condition differs from the balanced flow by setting the damper 54 so that the blower 44 discharges more air than is being supplied to the work area by the blower 46. As a result of discharging a quantity of air greater than the quantity supplied, air is aspirated into the work area through the opening 19. This air, which is relatively dirty, enters into the work area only a couple of inches before it is drawn into the floor 21. Air inflow condition is often advantageous when working with highly toxic substances in that the relatively small quantity of the entrained air further assures against the escape of the toxic particles or fumes. The air outflow condition, on the other hand, is essentially opposite to the air inflow condition in that the blower damper 54 is set to provide the discharge of less air than is being supplied by the supply blower 43. Consequentially, the excess air delivered to the work area 18 passes out the opening 19. Normally, this type flow condition is less preferable than the other two, but in some instances, such as when the window or panel 40 is fully opened, it may be satisfactory because of its capabilities in preventing contamination products from entering the work area. The air during an outflow condition retains the laminar flow characteristics with substantially all the air being passed through the floor 21 except for the portion of the air flow adjacent the opening 19. This portion of the air flow does not abruptly pass through the opening 19 upon emerging from the filter 25, but tends to travel in a slanting vertical direction such that the air passes from the work area adjacent the floor 21 and thereby assuring that any airborne contaminants from outside the work area that by chance are picked-up by the air flow will not be deposited upon the materials or items in the work area 18. Of .course, the quantity of air passing through the opening 19 and the slant or angle of the air flow are dependent upon several operating conditions, e.g., the setting of the damper 54, the size of the opening 19, quantity and velocity of air being passed through the work area 18, etc. Thus, even with outflow conditions a highly toxic substance may be utilized in the work area if it is spaced a sufficient distance inwardly from the opening 19.

In order to better understand the present invention, a detailed description of a vented hood assembly constructed substantially similar to the arrangement shown in FIGS. 1-3 is hereinafter set forth; of course, bearing in mind that while the general operating principles and arrangement of components remain essentially the same for any vented hood assembly constructed in accordance with the teachings of the present invention, the particular characteristics, e.g., air volume and velocity, blower arrangement, overall dimensions, and the like, may be different for each assembly.

A vented hood assembly may have outside dimensions of 8 1 inches in height, 40 inches in width and 27 inches in depth, while the inside dimensions, i.e., the work area 18, may be 20 inches in height, 28 inches in width and 23 inches in depth. The filter 25 may be 24 inches wide, 30 inches long, and about l l inches high such that when the filter is placed in position essentially the entire ceiling of the work area 18 consists of the effective filter portion 2'7.

The air supply and exhaust blowers 43 and 44 respectively, may be of similar capacities; for example, blowers found satisfactory may be of about five-eights horsepower and capable of moving air at about 1160 cubic feet per minute (c.f.m.) at one-half inch static water pressure and 940 c.f.m. at one inch static water pressure. The supply blower 43 may be preferably held at a substantially constant output, i.e., within the above noted capacities, while the exhaust blower 44 may be provided with the damper 54 and damper adjustment mechanism (not shown). The average air flow in the noted assembly may be about feet per minute (ft/min.) with a minimum flow of about 145 ft./min. and a maximum flow of about ft./min. Adjustments of the damper 54 to give an air flow of about 100 ft./-min. out the opening 19 with the window or panel 40 opened about 8 inches and an air flow of about 100 ft./min. into the opening 19 with the panel 4!) opened about 8 inches has no appreciable effects on the above air flow velocities.

In order to determine the quantity of airborne particulate matter O.32 micron and larger per cubicfoot of air in the work area, a series of tests may be run at various flow conditions and panel openings. A suitable sensing device such as Royco particle counter PC-ZOOA may be used for these tests with the Royco probe placed at a location within the work area at least four inches away from the opening 19 and with the panel 40 being opened about eight inches.

Results of tests made with a Royco particle counter in one instance are as follows:

Particles 0.32 micron or larger,

Condition of Test total per cubic foot When operating the assembly with a fully opened panel 40, i.e., at least inches or the height of the work area, it may be preferable to use an air outflow of about ft./min. However, if the work is to be accomplished at distances greater than six inches inside the work area 13, then a balanced air flow condition may be satisfactorily used.

The above described assembly not only maintains an extremely clean working environment, but also provides excellent isolation properties for noxious fumes generated in the work area 1 8. For example, a toxicity test run with the panel opened eight inches and with the assembly set to provide an outward air flow of about 100 ft./min. (considered the worst possible conditon under which the hood would be operated) provided the results following.

An 8 inches by 10 inches by 2 inches deep container filled with trichlorethylene (a toxic cleaning solvent) was placed on the center of the floor 21 and six pads soaked with trichlorethylene were randomly scattered throughout the work area 18 with two of these pads being within four inches of the hood opening 19. A test using the well known Kitagawa principles, which are capable of measuring trichlorethylene in concentrations of :10 to 400 parts per million of air, was used to determine the quantity of trichlorethylene vapors escaping through the opening 19. The maximum permissible concentration of trichlorethylene for health safety is set at 100 parts per million of air by the American Conference of Governmental Hygienists. However, even with the aforementioned worst operating conditions only a trace of trichlorethylene representing somewhat less than 10 parts per million of air was detected outside the opening 19.

The ventilating system of the present invention may be provided with equipment for using solvents, e.g., trichlorethylene, such as shown in FIG. 5. A cleaning tank such as an ultrasonic cleaner shown generally at 56 may be placed in the work area 18 in any desired location. For example, the cleaner 56 may be placed in an opening through the floor 21 such that only the uppermost edge or surface remains in the work area. The laminar air flow through the work area 18 is essentially unaffected by the obstruction provided by the cleaner 56 in that the air substantially vertically approaches a location very near the surface of the cleaner 56 before it is sharply turned in a substantially horizontal direction as indicated by the arrows. This turned air is pulled through the floor 21 as it passes over the marginal edges of the cleaner 56, thus preventing an undesirable horizontal air flow condition which may force noxious fumes through the opening 19.

When using cleaning solvents or other liquids or substances in the work area 18 it may be desirable to assure against collecting such agents in the compartment 38 or spilling such agents into the opening of the exhaust blower 44. Satisfactory results in this area have been attained by slanting the partition 22 towards the rear wall 14 so that these agents may be passed through a suitable drain arrangement such as shown at 57 ('FIG. 2). Also, the blower 43 may be protected by placing a suitable splash cover 58 over the inlet.

FIG. 6 shows another form of the present invention that may be advantageously used when working upon relatively minute items. In this form a substantial centrally located portion of the floor 21 may be made relatively imperforate such that perforated marginal portions or edges of the floor provide the communication with the exhaust blower 44. The air flow pattern with this arrangement is somewhat similar to the air flow pattern in the FIG. 5 form in that the air nearly reaches the surface of the floor 21 before it is sharply turned, thus minimizing turbulence in the upper portions of the work area 18.

FIG. 7 shows still another form of the present invention in which the entire floor 21 within the vertical con-fines of the work area 18 may be made imperforate, for providing a larger Work space than the form shown in FIG. 6. The work area linings 30a, 31a, and 32a, corresponding to linings 30-32 in FIGS. 16, may be terminated at a location upwardly spaced from the floor 21 while wall I la, corresponding to wall 11 in the previous figures, may have a portion thereof extending above the floor level and spaced outwardly from the upper portion of the wall 11a containing the panel 46". With this arrangement the laminar air traverses the Work area in a manner substantially similar to that in FIG. 6 embodiment except, in this form, the air passes in an essentially horizontal direction from the vertical confines of the work area.

It will be seen that the present invention sets forth many advantages or features, e.g., the working with poisonous substances need no longer be so difficult or dangerous, and the heretofore always present problems resulting from contamination or excessive airborne particles in the working environment are essentially eliminated. Another use for the present invention may be in clean rooms such as disclosed in applicants above noted copending application for removing residue from grinding, soldering, and welding operations which may be carried out in the clean room. Also instead of using the damper 54 in the exhaust blower duct-work, it may be desirable to use a variable capacity blower. If desired, a single motor with a pair of air moving means, one of which may be regulated, may be used in place of the two blower system above disclosed. Another feature of the invention may be attained in the area of environmental control in that suitable dehumidifying, humidifying, air-conditioning or heating means may be placed in the cabinet or in some association with the cabinet such as in a remote air source.

As various changes may be made in the form, construction and arrangement of the parts herein without departing from the spirit and scope of the invention and without sacrificing any of its advantages, it is to be understood that all matter herein is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. A laminar flow air hood apparatus comprising the combination of generally upright wall means substantially surrounding a space, a generally horizontally disposed submicron air filter substantially filling a cross-sectional space within confines of said wall means adjacent upper portions thereof, a top member spaced above the air filter and joined with said wall means forming with the latter and an uppermost surface of the air filter a plenum chamber, a platform below and spaced from the air filter, said wall means including portions forming an air inlet passageway communicating with the plenum chamber and portions spaced inwardly from and extending generally along outer portions and forming with the filter and platform a work chamber, at least part of the wall means below the air filter and adjacent the platform being displaceable to provide an opening for ingress and egress of the work chamber, a third chamber or sompartment extending below said Work chamber and platform, partition means forming a lower boundary of the third chamber extending generally between the wall means, .a fourth chamber below said third chamber and partition, a lower end wall forming a bottom of the fourth chamber, a second air filter in the fourth chamber, first blower means in the fourth chamber for drawing air through the second air filter and discharging it to said inlet passageway and said plenum chamber to flow through said sub-micron air filter and downwardly as a body of air moving substantially parallel to said inwardly spaced portions of the wall means and with said body of air traversing the work chamber below the sub-micron filter in an essentially uniform manner and velocity throughout substantially all cross sections of the work chamber, passageway means providing communication between the Work chamber and the third chamber, second blower means in the fourth chamber for drawing air through the passageway means and discharging it external of the assembly, means for selectively controlling the quantity of air discharged by the second blower means independently of the quantity of air supplied by the first blower means to provide a balanced air fiow condition or an air inflow condition via said opening or an air outflow condition via said opening, and an outlet drain from said third chamber for discharging fluids from the third chamber.

2. The apparatus of claim 1 wherein the passageway means comprises a plurality of perforations through the platform and disposed substantially throughout the area thereof.

3. The apparatus of claim 2 wherein the platform has an opening therethrough substantially larger than any of said perforations and container means are disposed within said opening with an upper surface thereof adjacent the upper surface of the platform.

4. The apparatus of claim '1 wherein the passageway means comprises a plurality of perforations through the platform adjacent marginal portions thereof.

5. The apparatus of claim 1 wherein the inwardly spaced portions of the wall means have end portions terminating at a location upwardly spaced from the platform.

References Cited by the Examiner UNITED STATES PATENTS 746,832 12/ 1903 Hecker 312-44013 X 1,211,325 1/1917 Lilly 98-115 2,291,220 7/ 1942 Germonprez. 2,704,505 3/ 1955 Morrison 98-115 2,709,954 6/ 19551 Baker. 3,097,587 7/1963 Kurek 98-36 3,113,501 12/1963 Cargo. 3,158,457 11/1964 Whitfield 55472 3,168,030 2/ 1965 Wilhelmsson et a1. 981 15 OTHER REFERENCES Marsh: Laminar Air Flow For Contamination Control, Journal of American Association for Contamination Control, vol. 2, No. 5, May 1963, pp. 7-11.

ROBERT F. BURNETT, Primary Examiner. 

1. A LAMINAR FLOW AIR HOOD APPARATUS COMPRISING THE COMBINATION OF GENERALLY UPRIGHT WALL MEANS SUBSTANTIALLY SURROUNDNG A SPACE, A GENRALLY HORIZONTALLY DISPOSED SUBMICRON AIR FILTER SUBSTANTIALLY FILLING A CROSS-SECTIONAL SPACE WITHIN CONFINES OF SAID WALL MEANS ADJACENT UPPER PORTIONS THEREOF, A TOP MEMBER SPACED ABOVE THE AIR FILTER AND JOINED WITH SAID WALL MEANS FORMING WITH THE LATTER AND AN UPPERMOST SURFACE OF THE AIR FILTER A PLENUM CHAMBER, A PLATFORM BELOW AND SPACED FROM THE AIR FILTER, SAID WALL MEANS INCLUDING PORTIONS FORMING AN AIR INLET PASSAGEWAY COMMUNICATING WITH THE PLENUM CHAMBER AND PORTIONS SPACED INWARDLY FROM THE EXTENDING GENERALLY ALONG OUTER PORTIONS AND FORMING WITH THE FILTER AND PLATFORM A WORK CHAMBER, AT LEAST PART OF THE WALL MEANS BELOW THE AIR FILTER AND ADJACENT THE PLATFORM BEING DISPLACEABLE TO PROVIDE AN OPENING FOR INGRESS AND EGRESS OF THE WORK CHAMBER, A THIRD CHAMBER OR COMPARTMENT EXTENDING BELOW SAID WORK CHAMBER AND PLATFORM, PARTITION MEANS FORMING A LOWER BOUNDARY OF THE THIRD CHAMBER EXTENDING GENERALLY BETWEEN THE WALL MEANS, A FOURTH CHAMBER BELOW SAID THIRD CHAMBER AND PARTITION, A LOWER END WALL FORMING A BOTTOM OF THE FOURTH CHAMBER, A SECOND AIR FILTER IN THE FOURTH CHAMBER, FIRST BLOWER MEANS IN THE FOURTH CHAMBER FOR DRAWING AIR THROUGH THE SECOND AIR FILTER AND DISCHARGING IT TO SAID INLET PASSAGEWAY AND SAID PLENUM CHAMBER TO FLOW THROUGH SAID SUB-MICRON AIR FILTER AND DOWNWARDLY AS A BODY OF AIR MOVING SUBSTANTIALLY PARALLEL TO SAID INWARDLY SPACED PORTIONS OF THE WALL MEANS AND WITH SAID BODY OF AIR TRAVERSING THE WORK CHAMBER BELOW THE SUB-MICRON FILTER IN AN ESSENTIALLY UNIFORM MANNER AND VELOCITY THROUGHOUT SUBSTANTIALLY ALL CROSS SECTIONS OF THE WORK CHAMBER, PASSAGEWAY MEANS PROVIDING COMMUNICATION BETWEEN THE WORK CHAMBER AND THE THIRD CHAMBER, SECOND BLOWE MEANS IN THE FOURTH CHAMBER FOR DRAWING AIR THROUGH THE PASSAGEWAY MEANS AND DISCHARGING IT EXTERNAL OF THE ASSEMBLY, MEANS FOR SELECTIVELY CONTROLLING THE QUANTITY OF AIR DISCHARGED BY THE SECOND BLOWER MEANS INDPENDENTLY OF THE QUANTITY OF AIR SUPPLIED BY THE FIRST BLOWER MEANS TO PROVIDE A BALANCED AIR FLOW CONDITION OR AN AIR INFLOW CONDITION VIA SAID OPENING OR AN AIR OUTFLOW CONDITION VIA SAID OPENING, AND AN OUTLET DRAIN FRON SAID THIRD CHAMBER FOR DISCHARGING FLUIDS FROM THE THIRD CHAMBER. 